Gynodioecy as a possible populational strategy for increasing reproductive output.

Cytoplasmic male steriles occur regularly in wild populations of the annual crucifer Hirschfeldia incana Lagr.-Foss. in Israel. In these plants numbers of ovules per flower, numbers of seed per fruit, and total seed weights per plant are slightly higher than in the hermaphrodites with which they mate. Yet their frequencies in wild populations do not exceed 2-10 per cent. There are no signs of incipient dioecy. The species is self incompatible and no mechanisms to enforce outcrossing are needed. It is argued that in this and similar cases gynodioecy functions as a pollen saving measure. Precise pollen presentation in the flower renders some of the pollen redundant and facilitates its abolition in a sector of the population. It is possible that the enhanced seed fecundity of the pollenless sector stems from a greater availability of plant resources for seed production in the unisexual than in the bisexual seed parent.